The present invention relates to a device comprising at least one element of aerodynamic shape, at least one Dart or zone of which can be folded up, for propulsion and/or lift using the effect of the relative wind. A device of this type is known inter alia from WO 86/00591 GRAVELINE.
More precisely, the invention relates to a device of the aforementioned type with great adjustable lift, which is intended for any craft which can be set in motion in the air, on water or on land, such as a boat, sailboard, aircraft, flying wing, kite, land yacht, etc. The invention is also applicable to the production of models of these locomotion or sport crafts.
Before going any further, for clear understanding of the prior art and of the invention, the meaning of expressions used in the present description and in the claims will be defined:
pressure face: (I--FIG. 1b) face of the element of aerodynamic shape which is at an increased pressure (in other words, face of the element which receives the wind);
suction face: (E--FIG. 1b) face of the element of aerodynamic shape at a reduced pressure;
leading edge: (BA--FIG. 1b) point, line, region furthest upstream of the element of aerodynamic shape, or of one of its parts or zones, viewed in the direction of the relative displacement of the air with respect to the said element;
trailing edge: (BF--FIG. 1b) point, line, region furthest downstream of the element of aerodynamic shape, or of one of its parts or zones, viewed in the direction of the relative displacement of the air with respect to the said element;
profile: shape of a cross-section of the element of aerodynamic shape taken in the direction of flow of the air,
skeleton of a profile: line connecting the leading edge to the trailing edge and passing between the pressure face and the suction face and at an equal distance from the latter:
chord of a profile: (CP--FIG. 1b) straight line connecting the leading edge to the trailing edge;
hollow of a profile: (C--FIG. 1b) maximum distance between the chord and the skeleton of a profile.
hauling point: linking point which can act as a moving control or fixing point.
There are known, for example from DE-1,531,328 LEMOIGNE, devices of the aforementioned type in which the said element has two faces designed to be located respectively on the pressure face side and the suction face side, at least one opening being provided to establish a passage of air from the pressure face side to the suction face side, and guide means being provided to direct the air emerging from the said opening on the suction face side, and give it a direction which is tangential to the said element.
The problem which is it sought to resolve by providing openings for the passage of air in such elements of aerodynamic shape is to prevent the boundary layer of the flow of air, on the suction face side, from "detaching" from the element in the region of the line of greatest hollow, which it tends to do when the element is curved. This detachment of the flow limits, and even decreases the aerodynamic performance. By allowing a passage of air from the pressure face to the suction face air is reinjected at a greater speed compared to that of the boundary layer which, thus reactivated, follows the aerodynamic shape of the element.
In doing so, however, it is necessary to avoid creating, especially on the suction face side, variations in shape which affect the aerodynamics of the element. Indeed, any alteration to this shape, however minimal this might be, generates disturbances in the flow of the boundary layer of air and promotes its detachment.
To improve the flow of the air, when the element of aerodynamic shape is a thick sail structure, LEMOIGNE proposes equipping such sail structures with traversing channels which are permanent means for guiding the air, which are materially defined by channel walls and whose cross-section decreases in the direction of the stream, the objective being thus to create a venturi tube. To the same end, where thin sails are concerned, LEMOIGNE proposes to equip them with nozzles which project greatly on the suction face side, hampering the profile of the sail structure in terms of aerodynamics.
For its part, U.S. Pat. No. 1,567,531 MAGNI describes a thick wing comprising a first part with a partially adjustable shape of curvature and a second part with an immovable shape of curvature, mounted so that it can pivot with respect to the said first part, it being possible for an air passage to be opened between these two parts, the opening/closing of the said passage being a function of the hollow of the wing (of the extent of the said pivoting) and the passage being delimited by two walls of immovable configuration respectively belonging to each of the two parts. The geometry of the air passage of this device is not adjustable: it always forms a divergent nozzle, which slows down the air.
The object of the present invention is to propose means which improve the flow of the air from the pressure face to the suction face, so that the air emerges on the suction face as a stream with the same direction and same sense as those of the overall flow on the suction face at the point of junction of the said stream and of the said overall flow, and this being:
whilst allowing the element to retain its aerodynamic shape (that is to say without discontinuity, without a hollow or any obstacle which, inter alia, forms a deflector), even when the passage of air is not taking place, when the aerodynamic element is only slightly curved for example,
and by applying a principle which is suitable for any element of aerodynamic shape, particularly both for thin sail structures and for thick sail structures.
This object is achieved in this sense that in the device according to the invention, the said opening and the said guide means of the said air passage are adjusted in terms of geometry and opening/closing by means capable of acting both on the position and on the geometry of at least a part and/or zone of the said device and the said device further comprises means designed to set the geometry of the said element, namely at least the curvature in terms of shape and in terms of hollow.
It is understood that the invention is distinguished from the prior art represented by MAGNI in this sense, that the means implemented by MAGNI to vary the position of the parts of its thick wing having an influence on the air passages are, themselves, incapable of furthermore varying the geometry of the said parts, or of varying only this geometry, whereas the present invention offers all these possibilities. What is more, it will be noted that the invention can be distinguished from LEMOIGNE and MAGNI by the fact that it does not use guide means existing permanently in their geometry for guiding and defining one or several air passages which the air can take, flowing from one face to the other of the aerodynamic element, but guide means which are created, in their geometry for guiding, solely when required to allow such a flow, the said guide means thus created being, in addition, adjustable, and this is independent of the shape of the curvature of the said element and of its hollow.
U.S. Pat. No. 2,984,199 GIEWALD describes a flexible sail structure with a thin profile made in three parts forming a sail structure plane regardless of its orientation with respect to the craft which it equips. The three parts are positioned in an immovable way by the spacing and the alignment of the region of their leading edge. As opposed to the present invention, the three parts of the GIEWALD sail structure cannot take part in setting the shape of the curvature because the leading edges do not have their own mobility which allows them to position themselves adjustably with respect to one another.
The air passage opening according to the invention may equally well be continuous or discontinuous (it is clearly understood that here this is a continuity or discontinuity in space, not in time).
Preferably, the inlet or outlet cross-section of the air passage, located at the end of a leading edge and/or of a trailing edge of a part or zone of the element is substantially perpendicular (1) to the streamlines of the flow of air going from the pressure face to the suction face and (2) to the pressure face or the suction face at the point of the inlet or outlet cross-sections.
The position and the geometry of the opening may be adjustable and this position may be independent of the side of the concavity resulting from the curvature. One of the possible settings is obtained by displacing parts or zones of the element of aerodynamic shape with respect to one another in longitudinal or transverse directions or in rotation, in a plane perpendicular to the element and/or to its parts or zones, by pulling a leading edge and/or a trailing edge of the said element, part or zone and/or the respective region of these edges.
The setting of the geometry of the slits may be carried out without changing the positioning of the trailing edge formed by the means for guiding the stream of air which passes through the said opening.